On Wed, Sep 15, 2010 at 12:24 PM, Dave <e...@dc9.tzo.com> wrote: > Stuart: > > Didn't Cradek just do this?? ... the tach simulation with some Mesa > controls on his Mori Jr mill? > > So your drives do not require the commutation signals that on some Fanuc > systems was derrived from the encoder on the motor via the controls?? > these drives do derive the tach signal from an encoder on the motor
> > I never really fully understood the Fanuc commutation dilemma as I don't > have any Fanuc equipped machines. Skyko used to sell a little converter > board that would make the commutation signals for a Fanuc drive based on > the rotor position that > was detected by the motor encoder. > > I know that was an issue on some retrofits. > > Dave > > On 9/15/2010 9:22 AM, Stuart Stevenson wrote: > > On Wed, Sep 15, 2010 at 12:07 AM, Jon Elson<el...@pico-systems.com> > wrote: > > > > > >> Stuart Stevenson wrote: > >> > >>> Gentlemen, > >>> The servo amps on the Enshu have different accel/decel shapes. The > >>> PID.output trace has a sharp corner to it. The trace raises a little > and > >>> then turns almost straight up. The decel trace is MUCH more rounded. > Does > >>> this sound like an amplifier problem? > >>> > >>> > >> Not necessarily. It may just be a symptom of friction. During > >> acceleration, the motor > >> is not only accelerating the mass, it is also fighting the friction of > >> the slide, both have the same > >> mathematical sign. On deceleration, it must fight the mass of the > >> table, which exactly > >> mirrors the accel condition, BUT the friction is now of opposite sign, > >> and is HELPING > >> the deceleration. So, you can't perfectly optimize FF2 to cover both > >> conditions. > >> > >> > > once again pictures trump words - my explanation was not correct as you > will > > see > > the acce/decel look the same but the beginning and ending phases of each > are > > not balanced > > and the trace is the axis following error not the PID.output - I should > have > > said PID.error and axis following error - I had looked at the output > trace > > so that must have been stuck in one of the holes in my head > > > > > >> I wouldn't look at the PID.output, but just at following error, and set > >> FF2 to balance > >> the error of the two situations. If you have large discontinuities at > >> the accel/decel > >> time, then you may have to reduce acceleration in the .ini file, you may > >> be asking for > >> too much accel. > >> > >>> I am thinking it would be possible to convert this Fanuc amp to a > >>> > >> simple > >> > >>> amp by fooling the tach feedback. This servo amp accepts the encoder > >>> feedback on two terminals and converts these two signals into a tach > >>> > >> voltage > >> > >>> for comparison to the velocity signal. Would it be possible to do one > of > >>> > >> two > >> > >>> things to convert it to a simple amp with no tuning to the motor. > >>> I think the best way would be to find where the chip ouputs the > >>> > >> matching > >> > >>> tach voltage and connect the velocity signal voltage at that point. The > >>> > >> amp > >> > >>> would think the motor is following the signal perfectly and require no > >>> output adjustment. > >>> > >>> > >> Well, I happen to think a real velocity servo amp is just about > >> unbeatable. It does require > >> some more tuning than some other systems, but can be expected to perform > >> better under > >> a wide variety of conditions. > >> > >> > > so far in my world a Fanuc servo system is about as real as you can get > > I don't think it is any better than what EMC can do and maybe not as good > > and certainly not (by me) as adjustable. > > I have no way of adjusting any parameters on these amps. There are some > pots > > and jumpers. > > Does anyone know how to change the parameters without using a Fanuc > control? > > Does anyone have the information explaining the jumpers and pots? I have > > some information about the pots but nothing about the jumpers. > > > > > > > >>> or > >>> I could use an ADC to accept the velocity signal and generate an > >>> > >> encoder > >> > >>> pulse to match what would be seen as feedback from the motor. > >>> Either way this feedback would be perfectly matched to the input. > >>> EMC2's tuning would then have complete and total control of the > servo > >>> motor (axis motion) > >>> > >> Not sure how an analog-digital converter would be used here. More > >> likely, you'd need > >> > >> > > This Fanuc servo system has a servo amp that accepts: > > an analog velocity signal from the control > > digital signals to close the loop from the motor - an encoder on the > motor > > sends pulses to the servo and the control > > The Fanuc servo motor has no tach. > > > > I propose using an ADC to convert the analog velocity signal to a pseudo > > encoder pulse to replace the motor feedback. > > I think this would remove the tuning from the servo amp as the amp would > see > > the motor as perfectly following the velocity signal at all times. > > Even better would be to shunt the velocity signal directly to the tach > > signal the chip on the control generates. > > Even better would be to disable the internal tuning by shifting jumpers. > > Maybe (I am not sure) better would be to have a procedure to tune the > amps > > and motors as a unit. This may be better but I don't like it as well as > any > > of my other thoughts. > > > > a digital to analog converter to produce the simulated tach signal. > > > >> But, most servo amps > >> can be converted to torque mode, usually by pulling a jumper that > >> bypasses the > >> velocity error amp. But, I still feel that a velocity servo with a real > >> tach should work > >> well, and you need a VERY high resolution encoder to move smoothly > >> without a tach. > >> > >> Maybe you could post the trace you are concerned about. > >> > >> > > pictures are here > > http://www.mpm1.com:8080/machines/enshu > > > > there are pictures of all three axes both positive and negative moves > > thanks > > Stuart > > > > > > > > ------------------------------------------------------------------------------ > Start uncovering the many advantages of virtual appliances > and start using them to simplify application deployment and > accelerate your shift to cloud computing. > http://p.sf.net/sfu/novell-sfdev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- dos centavos ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
